Embodiments herein generally relate to printing devices and, more particularly, to a velocity matching calibration method for multiple sheet transport devices within a sheet transport path of a printing device.
Printing devices typically incorporate multiple independently driven sheet transport devices along a sheet transport path. Specifically, such sheet transport devices can include, but are not limited to, electrostatic transport belts, nip apparatuses, registration systems, fusers, etc., each having a servo-controlled drive roller. With such independently driven sheet transport devices, velocity matching can become critical in order to avoid errors (e.g., registration errors, image on image transfer errors, etc.), particularly when a transported sheet (e.g., a transported sheet of paper) spans across and is simultaneously engaged by multiple sheet transport devices. Current drive schemes try to minimize these errors by using, for each sheet transport device, a servomechanism with a very tight tolerance to accurately control power supplied to the motor which rotates the drive roller and, thereby to accurately control the linear velocity of the sheet being transported. Unfortunately, when a single sheet is simultaneously engaged by two independently driven adjacent sheet transport devices, any velocity discrepancy between the two devices will cause contention between the servomechanisms. During such contention, the servomechanisms for the sheet transport devices essentially “fight” for velocity control, which can cause a mismatch between the velocity of the leading edge of the sheet and the trailing edge as they pass a given point. For example, consider a sheet being transported along a path between a preceding sheet transport device and a following sheet transport device. When the servomechanisms of the sheet transport devices are in contention, the sheet, as it passes a point along the path, will have a certain velocity equal to either that of a dominating transport if slippage occurs in the other contending transport, a differential velocity if sheet buckling occurs, or some velocity equilibrium between the contending transports. When the sheet is finally output from the preceding sheet transport device such that the servomechanisms of the two sheet transport devices are no longer in contention, the velocity of the sheet could momentarily spike up or down from accumulated servo positional error. Such velocity variations can result in the same errors that the servomechanisms were designed to avoid (e.g., registration errors, image on image transfer errors, etc.).
In view of the foregoing, disclosed herein are embodiments of a method that incorporates calibration and printing operations to be used with a printing device. The printing device contains a sheet transport path with multiple adjacent sheet transport devices (e.g., electrostatic sheet transport belts, nip roller apparatuses, registration systems, fusers, etc.), each having at least one independently controlled drive roller. Each preceding sheet transport device feeds a sheet to a following sheet transport device along the path in succession. Furthermore, two or more adjacent sheet transport devices are positioned to simultaneously engage the sheet as it is being transported along the path. The calibration operation is used to determine the particular drive roller angular velocity that should be used by each sheet transport device to compensate for drive roller contention during the printing operation and, thereby to ensure that the linear velocity of the sheet essentially remains constant as it is transported across each adjacent transport throughout the printing operation.
More particularly, one embodiment of the method comprises performing a calibration operation for adjacent sheet transport devices within a sheet transport path of a printing device and also performing at least one printing operation using the printing device.
This calibration operation comprises transporting a test sheet along the path. When the test sheet is simultaneously transported by contacting both a first sheet transport device and a second sheet transport device that is positioned adjacent to the first sheet transport device in the path (i.e., when the sheet is simultaneously engaged by or acted upon by both the first and second sheet transport devices in order to move the sheet towards the end of the path), then a constant power mode (i.e., a torque assist mode) is used to rotate a first drive roller of the first sheet transport device. Additionally, a constant velocity mode is used to rotate a second drive roller of the second sheet transport device at a predetermined angular velocity. This predetermined angular velocity at which the second drive roller is set is determined prior to the calibration operation (e.g., by a user or by default based on a desired sheet velocity). As a function of these different modes, the second sheet transport device alone controls the linear velocity of the sheet and drive roller contention does not occur. As the first drive roller is rotated during the constant power mode, its actual angular velocity can be determined. The determined angular velocity can subsequently be used during the printing operation to compensate for drive contention.
Once the calibration operation is completed, one or more printing operation can be performed. Each printing operation comprises transporting a print sheet along the path. When the print sheet is transported by both the first sheet transport device and the second sheet transport device, then the constant velocity mode is used to rotate the first drive roller at the angular velocity that was determined for that first drive roller during the calibration operation. Additionally, the constant velocity mode is again used to rotate the second drive roller at the predetermined angular velocity. As a result of the calibration operation, drive contention is compensated for and the linear velocity of the print sheet used in the printing operation will essentially remain constant across the adjacent transport devices.
In another embodiment, the calibrated angular velocity used during the printing operation is a mean angular velocity based on multiple calibration passes rather than a single calibration pass in order to compensate for AC errors (i.e., errors due to belt thickness variations or the like, which are substantially consistent between belt revolutions). Specifically, this embodiment similarly comprises performing a calibration operation for adjacent sheet transport devices within a sheet transport path of a printing device and also performing at least one printing operation using the printing device.
The calibration operation comprises transporting multiple test sheets in succession along the path. Then, for each test sheet, the following calibration processes are performed. When the test sheet is transported by both a first sheet transport device and a second sheet transport device adjacent to the first sheet transport device in the path (i.e., when the sheet is simultaneously engaged by or acted upon by both the first and second sheet transport devices in order to move the sheet towards the end of the path), then a constant power mode is used to rotate a first drive roller of the first sheet transport device. Additionally, a constant velocity mode is used to rotate a second drive roller of the second sheet transport device at a predetermined angular velocity. This predetermined angular velocity at which the second drive roller is set is determined prior to the calibration operation (e.g., by a user or by default based on a desired sheet velocity). As a function of these different modes, the second sheet transport device alone controls the linear velocity of the sheet and drive roller contention does not occur. Then, as the first drive roller is rotated, its actual angular velocity can be determined. This process is repeated with each of the multiple test sheets. Then, using the multiple angular velocities determined with each calibration pass, a mean angular velocity is determined. The determined mean angular velocity can subsequently be used during the printing operation to compensate for drive contention.
Once the calibration operation is completed, one or more printing operations can be performed. Each printing operation comprises transporting a print sheet along the path. When the sheets are transported by both the first sheet transport device and the second sheet transport device, then the constant velocity mode is used to rotate the first drive roller at the mean angular velocity that was determined for the first drive roller during the calibration operation. Additionally, the constant velocity mode is again used to rotate the second drive roller at the predetermined angular velocity. As a result of the calibration operation, drive contention is compensated for and the linear velocity of the print sheet used in the printing operation will essentially remain constant across the adjacent transport devices.
In another embodiment, the method takes into account a situation where the printing device comprises three or more adjacent sheet transport devices within the sheet transport path and where the sheet transport devices are positioned in series such that sheets moving through the path may be transported by two of the sheet transport devices at a time. Specifically, this embodiment comprises performing a sequential calibration operation for at least three adjacent sheet transport devices within a sheet transport path of a printing device and also performing at least one printing operation using the printing device.
The sequential calibration operation comprises transporting at least one test sheet along the path. Then, each pair of the adjacent transport devices in the path is separately and sequentially calibrated, in either a first order beginning from the end of the path or a second order beginning from the start of the path. It should be understood that the pairs of transport devices sequentially overlap such that they all contain a transport device from at least one immediately adjacent pair
During calibration, when a test sheet is transported by both a first sheet transport device and by a second sheet transport device that is adjacent to the first sheet transport device in a given pair (i.e., when the sheet is simultaneously engaged by or acted upon by both transport devices in a given pair in order to move the sheet towards the end of the path), then a constant power mode is used to rotate a first drive roller of the first sheet transport device. Additionally, a constant velocity mode is used to rotate a second drive roller of the second sheet transport device at a predetermined angular velocity. It should be noted the relative position of the “first sheet transport device” and the “second sheet transport device” within the path for purposes of performing the calibration operation varies depending upon whether the calibration operation is being perform in the first order or in the second order. Specifically, when the calibration operation is performed in the first order (i.e., beginning from the end of the path), then the second sheet transport device follows the first sheet transport device within the path. Contrarily, when the calibration operation is performed in the second order (i.e., beginning from the start of the path), then the second sheet transport device precedes the first sheet transport device within the path.
As a function of these different modes, the second sheet transport device in the given pair alone controls the linear velocity of the sheet and drive roller contention does not occur. Then, as the first drive roller in the given pair is rotated, its actual angular velocity is determined. Optionally, rather than determining the angular velocity based on one calibration pass, multiple calibration passes can be performed and a mean angular velocity for the first drive roller of each pair can be determined. The determined angular velocity (or determined mean angular velocity) can subsequently be used during the printing operation to compensate for drive contention.
As mentioned above, this process is repeated for each pair in either the first order or the second order. It should be noted that, during calibration of the first pair in the order, the predetermined angular velocity at which the second drive roller is set is determined prior to the calibration operation (e.g., by a user or by default based on a desired sheet velocity). It should also be noted that, as mentioned above, the pairs of transport devices sequentially overlap such that they all contain a transport device from at least one immediately adjacent pair. Thus, with each subsequently calibrated pair, the second drive roller is actually the first drive roller of an immediately adjacent and previously calibrated pair and the predetermined angular velocity that should be used for the second drive roller is the previously calibrated angular velocity (i.e., is that angular velocity determined for the first drive roller during calibration of the immediately adjacent and previously calibrated pair).
Once the calibration operation is completed, one or more printing operations can be performed. Each printing operation comprises transporting a print sheet along the path. When the print sheet is transported along a given pair, then the constant velocity mode is used to rotate the first drive roller at the angular velocity (or mean angular velocity) that was determined for the first drive roller during the calibration operation. Additionally, the constant velocity mode is again used to rotate the second drive roller at the predetermined angular velocity. As a result of the calibration operation, drive contention is compensated for and the linear velocity of the print sheet used in the printing operation will essentially remain constant across the adjacent transport devices.
Another embodiment of the method takes into account a situation where the printing device comprises three or more adjacent sheet transport devices within the sheet transport path and where the sheet transport devices are positioned in series such that sheets moving through the path may be transported by a set of three or more of the sheet transport devices at a time. As with the previously described embodiments, this embodiment comprises performing a calibration operation for the adjacent sheet transport devices within a sheet transport path of a printing device and also performing at least one printing operation using the printing device.
The calibration operation comprises transporting at least one sheet along the path. Then, each set of the adjacent sheet transport devices, which will simultaneously engage a sheet being transported along the sheet transport path, is separately and sequentially calibrated in either a first order beginning from the end of the path or a second order beginning from the start of the path. It should be understood that the sets of transport devices sequentially overlap such that they all contain transport devices from at least one immediately adjacent set.
During calibration, when a test sheet is transported by all sheet transport devices in a given set (i.e., when the sheet is simultaneously engaged by or acted upon by all transport devices in a given set in order to move the sheet towards the end of the path), a constant velocity mode is used to rotate a single drive roller of a single transport device in the given set at a predetermined angular velocity. Additionally, a constant power mode is used to rotate any other drive rollers of any other transport devices in the given set. It should be noted the relative position of the “single transport device” and the “any other transport devices” within the path for purposes of performing the calibration operation varies depending upon whether the calibration operation is being perform in the first order or in the second order. Specifically, when the calibration operation is performed in the first order the single transport device follows, within the path, any other transport devices of a set. Contrarily, when the calibration operation is performed in the second order the single transport device precedes, within the path, any other transport devices of a set.
As a function of these different modes, the single transport device in the given set alone controls the linear velocity of the sheet and drive roller contention does not occur. Then, as the other drive rollers are rotated, their corresponding angular velocities are determined. Optionally, rather than determining the corresponding angular velocities based on one calibration pass, multiple calibration passes can be performed and corresponding mean angular velocities for these other drive rollers within each set can be determined.
As mentioned above, this process is repeated for each set in the selected order. It should be noted that, during calibration of the first set in the order, the predetermined angular velocity at which the single drive roller is set is determined prior to the calibration operation (e.g., by a user or by default based on a desired sheet velocity). It should also be noted that, as mentioned above, the sets of transport devices sequentially overlap such that they all contain transport devices from at least one immediately adjacent set. Thus, with each subsequently calibrated set, the predetermined angular velocity that should be used for the single drive roller is determined during calibration of the immediately adjacent and previously calibrated set.
Once the calibration operation is completed, one or more printing operations can be performed. Each printing operation comprises transporting a print sheet along the path. When the print sheet is transported along each given set, the constant velocity mode is used to rotate the single drive roller in that given set at the predetermined angular velocity. Additionally, the constant velocity mode is used to rotate any other drive rollers from any other sheet transport devices in that given set at their corresponding angular velocity, as determined during the calibration operation. As a result of the calibration operation, drive contention is compensated for and the linear velocity of the print sheet used in the printing operation will essentially remain constant across the adjacent transport devices. Furthermore, as discussed above, using corresponding mean angular velocities determined based on multiple calibration passes will compensate for (i.e., essentially zero out) AC errors.
In each of the above-described method embodiments, it should be understood that the constant power mode (i.e., the torque assist mode) and constant velocity mode are different modes by which actuators (e.g., servo drivers of servomechanisms) control the motors (e.g., servo motors) for the drive rollers and, thereby control the drive rollers of the different sheet transport devices. For example, in the constant power mode a constant level of power is supplied to a specified motor of a specified drive roller in order to approximately achieve a pre-set angular velocity. Alternatively, in the constant velocity mode an actual angular velocity of a specified drive roller is continuously or periodically determined and, based on the actual angular velocity, the level of power supplied to the specified motor of the specified drive roller is adjusted in order to maintain the specified driver roller at a pre-set angular velocity.
Also disclosed herein are embodiments of a computer program product comprising a computer usable medium having computer useable program code embodied therewith. This computer usable program code can be configured to perform the above described method embodiments.
These and other features are described in, or are apparent from, the following detailed description.